The invention concerns a process for the determination of iron in body fluids by release of the bound iron, reduction to Fe.sup.2+, addition of a chromogenic system suitable for the detection of iron and measurement of the complex with chromogen. The invention also concerns a reagent combination which is suitable for the measurement of lipaemic sera even without addition of mixtures of detergents to remove turbidity.
Disorders of iron metabolism, especially iron deficiency and disturbances in iron resorption, occur particularly commonly in the female population. Therefore, the determination of iron in body fluids, especially in serum, is one of the standard determinations in medical analysis. Iron is supplied with the food and is absorbed across the mucous membrane of the intestine. It is then transported, bound to transferrin in a trivalent state, to the bone marrow where it is mainly incorporated into haemoglobin. Absorption of too little iron can lead to anaemic symptoms.
The determination of iron in serum is one of the most frequently performed trace element analyses in clinical diagnosis. Various processes are known for this purpose. Thus in Clin. Chem. 26, (1980) 327-331 a process is described in which trivalent iron bound to transferrin in the form of a carbonate complex is released in a strongly acid medium. A disadvantage of this process is that the strongly acid reagents are caustic and corrosive. In order to overcome this disadvantage, it is known for example from Clin. Chem. 23, (1977) 237-240 and from Z. Klin. Chem. 3 (1965) 96-99 that protein denaturing agents such as concentrated guanidinium chloride or anionic detergents can be used to release the iron.
In the known embodiments of these processes errors in measurement occur when iron is determined in turbid lipaemic sera. Neither guanidinium chloride nor the anionic detergents have a sufficient clarification power to achieve a complete elimination of the turbidity.
In order to solve this problem the use of a mixture of non-ionic and anionic detergents to release the iron in a weakly acid medium was suggested in EP 130 537. However, it was found that, although the employment of these detergents results in a rapid and complete clarification of lipaemic sera, in sera with a high immunoglobulin content (gammopathy sera) an increase in turbidity is observed which can falsify the results of the measurements. Furthermore, the recovery of iron in strongly haemolytic sera is not completely satisfactory.
In addition, in all processes known up to now, a detergent must always be present either as denaturing agent or in order to avoid turbidity or to avoid interactions between chromogen and the sample. The presence of detergents is, however, disadvantageous in particular in the application of the methods on automatic analysers since detergents cause the formation of foam and can thereby considerably interfere with the measurements.